Improve context formatting in QuestionAnswerAdvisor

 - Add line breaks and clarify context boundaries in user text advice.
   This improve the performance of a Llama3.x
 - Update corresponding test to reflect new formatting

Author: tzolov

spring-ai-core/src/main/java/org/springframework/ai/chat/client/advisor/QuestionAnswerAdvisor.java

@@ -52,10 +52,13 @@
 public class QuestionAnswerAdvisor implements CallAroundAdvisor, StreamAroundAdvisor {
 
 	private static final String DEFAULT_USER_TEXT_ADVISE = """
-			Context information is below.
+
+			Context information is below, surrounded by ---------------------
+
 			---------------------
 			{question_answer_context}
 			---------------------
+
 			Given the context and provided history information and not prior knowledge,
 			reply to the user comment. If the answer is not in the context, inform
 			the user that you can't answer the question.

spring-ai-core/src/test/java/org/springframework/ai/chat/client/advisor/QuestionAnswerAdvisorTests.java

@@ -97,11 +97,13 @@ public void qaAdvisorWithDynamicFilterExpressions() {
 
 		assertThat(userMessage.getContent()).isEqualToIgnoringWhitespace("""
 			Please answer my question XYZ
-			Context information is below.
+			Context information is below, surrounded by ---------------------
+
 			---------------------
 			doc1
 			doc2
 			---------------------
+
 			Given the context and provided history information and not prior knowledge,
 			reply to the user comment. If the answer is not in the context, inform
 			the user that you can't answer the question.